EFFECT OF THE BLACK SIGATOKA RESISTANCE LOCUS BS(1) AND PLOIDY LEVEL ON FRUIT AND BUNCH TRAITS OF PLANTAIN BANANA HYBRIDS

Plantain (Musa spp., AAB group) cultivation is threatened by black sig atoka, an airborne fungal (Mycosphaerella fifensis Morelet) leaf spot disease. Several traits in plantains and bananas are mainly affected b y major genes. The host resistance response to black sigatoka is under the control of at least three different genes, one major recessive ge ne bs(1) and two other independent additive alleles. Diploid and tetra ploid plantain hybrids were evaluated for bunch weight, fruit weight, fruit length and fruit circumference. The F-1 euploid hybrids were der ived from interspecific crosses between the resistant diploid wild ban ana 'Calcutta 4' and the susceptible triploid plantain cultivars 'Obin o l'Ewai' and 'Bobby Tannap'. Linear and multiple regression models, c oefficients of determination, and Durbin-Watson statistics were used t o determine the single and combined effects of the major locus for bla ck sigatoka resistance and ploidy on the different traits in the proge nies. Differences in yield were mainly due to changes in weight and gi rth of fruit, which are affected by black sigatoka disease. The combin ed effect of ploidy and resistance to black sigatoka was partially res ponsible for the quantitative trait variation in yield. As a result of the gene interaction in the black sigatoka resistance locus bs(1), th e partially resistant and less susceptible phenotypes showed higher yi eld than their more susceptible full sibs.